Conventional diesel powered systems for engines, factories, and power plants produce emissions that contain a variety of pollutants. These pollutants may include, for example, particulate matter (e.g., soot), nitrogen oxides (NOx) such as NO and NO2, and sulfur compounds. Due to heightened environmental concerns, diesel powered engine exhaust emission standards have become increasingly stringent. The amount of pollutants in the flow of exhaust may be regulated depending on the type, size, and/or class of engine.
One method implemented by engine manufacturers to comply with the regulation of particulate matter exhausted to the environment has been to remove the particulate matter from the exhaust flow of an engine with a device called a particulate trap or diesel particulate filter (DPF). A DPF is a filter designed to trap particulate matter and typically consists of a wire mesh or ceramic honeycomb medium. However, the use of the DPF for extended periods of time may cause the particulate matter to build up in the medium, thereby reducing the functionality of the DPF and subsequent engine performance.
The collected particulate matter may be removed from the DPF through a process called regeneration. The regeneration process may involve elevating the temperature of the flow of exhaust to a high temperature using, for example, a burner or other heating device. The heated flow of exhaust may pass through the DPF, thus oxidizing the particulate matter trapped within the DPF. To achieve good regeneration results with a burner, sufficient air must be provided to the burner to achieve an acceptable equivalence ratio (equivalence ratio equals the actual fuel air ratio divided by the fuel air ratio required for stoichiometric combustion). As the amount of air relative to the amount of fuel increases, the equivalence ratio decreases.
One device for controlling combustion air input to a burner is described in U.S. Pat. No. 5,456,079 (the '079 patent) issued to Langen on Oct. 10, 1995. Specifically, the '079 patent discloses a device for thermal regeneration of particulate filters including a burner and a combustion air supply. The means for supplying combustion air to the burner preferably comprises a compressor or air pump or blower, respectively, that delivers a combustion air quantity per unit time that is dependent on the speed of the diesel engine (e.g., the quantity of combustion air per unit time is at least roughly matched to the speed of the diesel engine). The compressor may be driven mechanically by the diesel engine.
The '079 patent also discloses that there are regeneration situations in which it is advantageous for the '079 system not to be bound to the strict dependency of the combustion air quantity delivered by the compressor on the speed of the diesel engine. For taking such situations into account, a controllable valve is preferably provided between the compressor and the burner for controlling the combustion air quantity fed to the burner per unit of time.
Although the thermal regeneration device of the '079 patent may control combustion air input to a burner for regeneration, it may not achieve an acceptable equivalence ratio under some conditions, which may result in suboptimal regeneration results.
The disclosed systems and methods are directed to overcoming one or more of the problems set forth above and/or other problems in the art.